My expectation is that this is in the $3,000+ range for custom. You need a flat panel lift. As well, a mount which can telescope. The lift really is the hard part because you don't easily raise and lower a 75 pound display for years and years without some very significant infrastructure to the product. That will likely be a $2,000 lift. Then the articulated arm will likely be another $1,000 but will definitely be out there.
You probably would need some carpentry done to pit it all together nicely as well. IMO, if you don't intend to spend the money to do this one properly then I wouldn't recommend doing it at all. This is way to risky to do with sub standard product.